Through the degeneration of the vertebral disc, in particular of the vertebral disc nucleus (nucleus pulposus) a loss of height in the affected vertebral disc space often comes about which is connected with a loosening of the vertebral disc annulus (annulus fibrosus) and of the ligaments. Through this, the spinal column becomes instable at this location. The result is a horizontal displaceability of the vertebral bodies relative to one another (spondylolisthesis), which leads to impairments of the nerve roots in this region and/or of the spinal cord together with the pain resulting from this. Similar symptoms can arise after a chemo-enzymatic or physical (laser) disintegration of the vertebral disc nucleus (nucleolysis) for the treatment of a herniated disc (post-nucleolysis syndrome).
The principle for treating these symptoms consists in the surgical removal of the vertebral disc nucleus and the laying in or insertion respectively of one—in the region of the cervical vertebral column—or of two—in the region of the lumbar vertebral column—sufficiently stable bodies in order to restore the normal height of the vertebral disc space.
At the same time the horizontal displaceability must be prevented. This takes place either through the implant itself or through additional metal implants (instrumented fusion). These implants are subject in particular in the lumbar vertebral column to considerable forces, which can lead to the breakage of the metal implant. Therefore an attempt is made to have the intermediate vertebral insert grow together or fuse respectively as rapidly and as solidly as possible with the adjacent vertebral bodies.
Essentially two techniques are used for the treatment of patients with spinal trauma or degenerative disease of the spinal column.                1. Removal of the vertebral disc nucleus and of the cartilage at the end-plates, expansion of the intervertebral space to a normal width and insertion of a plano-parallel or horizontally slightly wedge-shaped block (Smith-Robinson technique).        2. Expansion of the vertebral disc space to normal height, drilling of a cylindrical opening which covers both vertebrae and insertion of a cylindrical dowel (Cloward technique). The dowel can in this connection either be a smooth cylinder or have the shape of a machine bolt.        
A relatively new method for the intercorporal fusion at the lumber vertebral column is the posterior lumbar intercorporal fusion in a unilateral transforaminal technique. In this connection, the foramen intervertebrale of the affected segment is opened unilaterally, the vertebral disc space is removed and, for the ventral support, two titanium lattice baskets are introduced which are cut to the matching height and which are filled with bone chips. This tissue-saving method does, however, have different disadvantages. On the one hand, the sharp edges of the titanium baskets can damage the nerve roots during introduction. Furthermore, no lordosiation is possible as the baskets are practically introduced blind. Finally, only the rims of the basket are available to absorb the pressure present. The titanium makes the fusion control more difficult due to artifacts and in computer tomography. Furthermore, the implant removal in revision operations is extremely difficult.
The object of the present invention therefore lies in providing an implant for the fusion of bones which eliminates the aforesaid disadvantages.